Movement of signs

In the geosemiotics of traffic signs, this warning slips between being 'situated' and 'transgressive' (Scollon & Scollon, 2003: 22). In some ways it only works in the upright position. I've often wondered then, at what stage in its history a sign of this sort can be said to loose its authority? When it is fallen, rusted or removed, or simply out of date, what it is intended to signify begins to wear away, as it comes to represent something else - something for which it was not originally intended. Around where I live, signs often disappear. I am reliably informed that they have good scrap value, and in times and places of economic hardship this counts for something. Their meaning value is exchanged for economic value. Ironically, the one in the picture is just outside a scrap yard - it's probably been displaced by a reversing heavy goods vehicle, but at this point in time nobody has cashed in. Perhaps this sequence of events contributes to a sense of the ambiguities surrounding text and context, and how these shift over time: is this, perhaps, another version of the traffic of texts?